Where do the numbers come from?

Why is a 303 fatter than a 308?

Did Communists use special commie calipers when they decided what size bullet to put in their 7.62 round?

Why are common revolver caliber designations exaggerated (you know what they call a 0.429" or that special 0.357" round).

Why were they correspondingly modest about what they called the old 0.585" calibers?

If a rifle takes 0.423" bullets, why is it called a 404?

H. C.

Henry, the numbers come from the fertile minds of the creators of the round.

308 win -- bore diameter
30-06 groove diameter and the year of introduction
303 -- brits on too much stout......
30/40 groove diameter and charge weight

22/250 - a "22 cal" based on the 250-3000 case.....

etc, etc, etc. Let it go. It'll drive you to drink if you let it..... JMO, Dutch.

I'm young and compared to many here relatively young... 19 with 15 years of shooting experience. Still, I've long since learned not to put too much thought into the numbers.. you'll give yourself a headache and be no closer to understanding.

Important thing is not to shoot ammunition in a gun unless the numbers of the case match the numbers on the barrel.

Be careful and shoot straight.

A major can o' worms, this. There are no rules, just general guides. American/British calibers tend to be named either for bore or groove diameter. Examples in inches:

By bore: .218 Bee, .218 bore (.223 or 4 groove). .30-06, .30/40, .30-30 are all .300 bore, .308 groove. .270 Winchester (.277 groove. .303 British, .303 bore, (.312 or so groove). .275 Rigby and .275 H&H Mag (.284 groove).

By groove: .308 Winchester (.300 bore), .257 Roberts (.250 bore), .284 Winchester (.275 bore), .224 Weatherby, .358 Winchester, .416 Remington.

Metrics can measure almost anything, as standardization didn't really occur until the 1960s if not later.

Then there are the somewhat bizarre mostly handgun cartridges like the various .38s shooting .357 diameter bullets and .44s with .429s. These almost all stem from cartridges that originally used bullets that were 'heeled' and outside lubricated, just like modern .22 long rifle ammo. The _case_ diameter is pretty much correct, in other words a .38 Special _case_ is about .380 in diameter just like a .38 short Colt, but the .38 short Colt uses a heeled bullet of .380 diameter while the .38 Special has an inside lubricated bullet that is enclosed by the case and consequently considerably smaller. The same with .44s, the .44 Mag traces its history back to the .44 S&W American (heeled .438 or so) and the .44 Russian - .44 Special (.429 inside lubed).

Then there are all the merely proprietary names that are sometimes maybe a bit close to some diameter, but not really: .222 Rem, .260 Rem, .280 Rem, .220 Swift, .225 Win, .378 Weatherby, .460 Weatherby. Goodness only knows why the .404 is named that, I think it was because it was so euphonious with .303...

All this merely scratches the surface, there a whole books written about cartridges and names.

With the revolver rounds, they were originally black powder, and used outside lubricated bullets, think of a 22 lr bullet, where the bullet is the same dia as the case. So, originally the 44 and 38 used 44 and 38 cal bullets. When the existing cases were used with inside lubed bullets, the caliber designation was retained, while the bullets shrank in dia.

If you want confusing, we have 219 zipper, 220 swift, 221 fireball, 222 rem, 223 rem, 224 weatherby and 225 winchester, and all fire a .224" dia bullet. Oh yeah, there is also a 220 russian that fires a .220" dia bullet!